Pulse width modulation (PWM) signaling is used in various electrical appliances to control driver circuitry for direct current (DC) motors. One problem encountered by a PWM signal generator is that the circuit is susceptible to switching noise generated by a switching controller in load circuitry, which creates undesired, extra pulses at the leading and trailing edges of the resulting PWM signal (known in the art as “chattering”), leading to unexpected or undesired operation of the PWM-controlled electrical circuit.
To counteract this problem, various techniques have been proposed to provide a noise-free, chatter-free PWM signal generator. For example, one conventional PWM signal generator includes a wave shaping circuit formed of a combinational logic circuit containing a feedback loop that feeds back an output signal to obtain a desired PMW signal without chattering.
The conventional PWM circuit described above, however, has several drawbacks. One drawback is that, since the output signal fed back to the wave shaping circuit has no initial value specified, the feedback loop can cause unexpected errors in other circuits connected to the shaping circuit. Moreover, a feedback loop included in the logic circuit is not desirable, because, in general, such inclusion can make it difficult to perform a logic synthesis where the entire circuitry is integrated onto a single integrated circuit (IC).
Another drawback is that the conventional wave shaping circuit cannot properly remove chattering components resulting from switching noise where the PWM signal has an extremely low or extremely high duty cycle. Not surprisingly, failure to properly remove undesired noise may cause errors and variations in the duty cycle of the resulting PWM output.